1. Field of the Invention
The present invention generally relates to an image forming apparatus.
2. Description of the Related Art
Conventional color image forming apparatuses include printers, copying machines, and facsimile machines. A color image forming apparatus includes image-forming sections that form yellow, magenta, cyan, and black images. Image forming sections are aligned in a direction in which a medium-transporting belt runs. As the medium-transporting belt runs through the image forming sections, yellow, magenta, cyan, and black toner images are transferred onto a print medium in registration with one another to form a full color toner image on the print medium. Then, the print medium is further advanced to a fixing unit where the print medium passes between a heat roller and a backup roller so that the full color toner image is fused into a permanent full-color image.
With a conventional image recording apparatus, the medium-transport belt can advance the print medium to the fixing unit at a somewhat higher speed than the circumferential speed of the heat roller. This small difference in speed creates slack in the print medium between the heat roller and the backup roller. The amount of slack depends on the length of the print medium. A long print medium will have a significant amount of slack therein and there is a possibility of the toner image formed on the print medium touching a chassis of the fixing unit. Thus, the toner image on the print medium can be damaged with the result that print quality is low.
The present invention was made in view of the aforementioned problems.
An object of the invention is to provide an image recording apparatus in which the print medium is prevented from contacting the chassis of the fixing unit and image quality is prevented from deteriorating.
An image recording apparatus includes an image forming section, a first medium-transporting section such as transport belt, a second medium-transporting section such as fixing roller and a discharge roller, and a controller. The image forming section forms a toner image on a medium. The first medium-transporting section transports the medium onto which the toner image has been transferred. The second medium-transporting section receives the medium transported from the first medium transporting section. The second medium-transporting section further transports the medium. The second medium-transporting section is disposed downstream of the first medium-transporting section with respect to a direction of travel of the medium. A controller controls at least one of a first transport speed of the first medium-transporting section and a second transport speed of the second medium-transporting section, so that a relative speed of the first medium-transporting section and the second medium-transporting section is changed. The second transport speed is changed relative to the first transport speed in accordance with a distance from a reference position over which the medium is advanced by the second transporting section toward the stacker.
The controller sets the second transport speed higher than the first transport speed when the medium has traveled over a distance longer than a predetermined length from the reference position.
If the medium has traveled over a predetermined distance after the controller sets the second transport speed higher than the first transport speed, the controller sets the second transport speed lower than the first transport speed.
The controller determines whether the medium has a length greater than a predetermined medium length. The controller changes the second transport speed by a predetermined fraction when the medium has a length greater than the predetermined medium length.
The image recording apparatus may further include a medium detector and a counter. The medium detector is disposed in a transport path of the medium to detect the medium, and the counter that counts operation parameters of the first medium-transporting section after the medium is detected by the medium detector. The controller checks an output of the counter to determine whether the medium is longer than the predetermined medium length.
The controller sets a second transport speed higher than the first transport speed when the medium has traveled over a distance longer than a predetermined length from the reference position.
The first medium-transporting section has a transfer section that transfers the toner image onto the medium. The second medium-transporting section has a fixing section that fixes the toner image on the medium.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.